x+y-z=0,3x+4y-z=0
2x+3y=0
x=-1.5y,z=-0.5y
x平方+xy+2z平方除以x平方-y平方
=(2.25y2-1.5y2-0.5y2)/ ( 2.25y2-y2)
=0.25 / 1.25
=0.2